I have defended my claims quite well.
You haven't defended why you say a country should be able to feasibly (and easily, as the mechanics will allow it as no restriction against such has been announced) develop a province like Orkney Islands into a province with the economic and military power of three of the largest cities in the game combined. The development mechanic needs further tweaks to prevent this situation occurring. You say that the mechanics as announced, with no single-province development soft caps, is a desirable outcome, and I don't think you've defended that at all well.
Yes, world conquest isn't immersive. But it's not a problem - because the AI does not do it. And a human player cannot do it without an immense amount of application and focus. Should that application and focus be applied, I continue to contend that it makes more sense for one global empire to extend it's control and influence over the entire world, then the extreme cases that these development mechanics with further reduced costs would enable. Heck, Spain and Britain could have got close if history had turned out a bit differently.
Single province uncapped development into the stratosphere is even more immersion-breaking - especially when that province might have a very small land base, and there might well be other reasons why supporting a very large development could not plausibly make any sense, such as climate, or being a minor state lacking the aggregated population to support such concentrations of economic power. And it's a problem because the AI will do it.
If you're going to disagree with my conclusions about these mechanics, say why you think it should be possible to build Orkney into a province with more economic power than Paris, Istanbul, and London combined. I say we can make further tweaks to prevent these extreme cases, while keeping the mechanic useful, fun, and balanced. Because you're playing an alternative history simulation game. You're not playing fricking Final Fantasy. We'll see what occurs, I guess.